Cellulose acetate and process of making same.



UNITED STATES PATENT OFFICE.

11mm? DREYFUS, or BASED, swrrznnnann.

CELLULOSE ACETATE AND PIBDCESS OF MAKING SAME.

no Drawing.

To all whom it may concern: I

Be it known that I, HENRY Dean-us, a citizen of the Republic of Switzerland, residin at Basel, Switzerland, have invented Cellu ose Acetates and Processes of Making Same, of which the following is a specification.

This invention relates to the manufacture by direct acetylation, of cellulose acetates insoluble in chloroform even on addition of alcohol, and also of cellulose acetates insoluble in chloroform but soluble therein on addition of alcohol; and also of theproducts of further transformation of these said acetates.

In French Patent No. 432046 and its addition 16494 and in my United States application 126502 filed October 19, 1916, and in my United States patent of February 27, 1917, No. 1217722, I have described a process of producing by direct acetylation, acetates of cellulose which are insoluble in chloroform, but soluble (and fpreferably easily soluble) by the addition 0 alcohol to the chloroform; also I have described the methods of transforming these roducts into products having other solubilities, b a later treatment, as described in said nited States application S. 126502.

According to the process of my application 103862, being partly a continuation of the present application, I have found also that acetates of cellulose can be produced by direct acetylation, which are insoluble in chloroform, which do not dissolve in chloroform on the addition of alcohol, even when warm although the may become plastic or semi-fluid in chloro orm on addition of alcohol.

These new direct acetylation products of my application 103862 are obtained if in the acetylation process, for example using sulfuric acid as a condensing agent, the acetylating mixture is cooled to a temperature as low as possible before introducing the cellulose to be acetylated and if the temperature is not thereafter allowed to rise above 20 or 25 C., the reaction being interrupted at the time when a test portion of the nearly clear solution demonstrates the insolubility in chloroform on addition of alcohol. If one allows the temperature to rise above 20 or 25 .C., products insoluble in chloroform are obtained, but these products are also soluble in alcohol-chloroform, and constitute Specification of Letters Patent.

Patented Oct. 8, 1918.

Application filed Kay 4, 191 5. Serial No. 25,820.

for example products 'of French Patent 432046.

In my application 103862 I have shown that the new products insoluble in chloroform and in alcohol-chloroform can be trans-' formed in the same manner which is indicated in lmy said United States Patent 1217722, into products havin other solubilities, if one submits the sai products to a later treatment, in their original acetylation solution, or in other appropriate solutions, with or without the addition of water, or acids or acid salts (ora mixture of two or more of these) and finally interrupting the reaction at the different phases, where the desired solubilities exist. The indications in detail, concerning the addition of water in certain proportions or other suitable bodies, or the changes brought about by the addition of acids, such as sulfuric acid, etc., are given in my co-pending application 126502, and accordingly it is not necessary to repeat the same here.

By this later treatment I have shown that one is able to obtain certain acetates of cellulose which even by the subsequent treatment do not become soluble in pure acetone, but remain as the products of departure soluble only in diluted acetone, while others possess a solubilityiin ure acetone.

On the other and I have also shown that in employing other condensing agents in stead of sulfuric acid, it is evident that the limits of temperature can be changed, and that for certain condensing agents, it is necessary even to apply heat for producing a reaction product having these properties. In other Words the temperature at this stage must be selected with reference to the condensing agent employed. Now I have found that neither for the production of cellulose acetates insoluble in chloroform but soluble upon addition of alcohol thereto, nor for the production of the cellulose acetates insoluble in chloroform and in alcohol-chloroform, has pure bisulfate of sodium which has been prepared in such a manner that it does not contain free acid, any acetylating action itself even at high temperatures, such as 70 C. The same is true for other acid salts of sulfuric acid, with the exception of the acid, sulfuric acid saltsof aromatic amins, such as bisulfate of anilin etc., which however possess no technical interest, since the solutions obtained therewith, as well as the products recipitated from these solutions become co ored owing to the oxidation of the aromatic amins. It is practically impossible to completely remove this coloration from the precipitated products.

I have found however that it is possible to effect the required acetylation even in the cold, with sodium bi'sulfate or other bisuL. fates (except bisulfates of aromatic amins) which contain more or less small quantities of free sulfuric acid. In order to attain this result, free sulfuric acid contained in an acetylating mixture (e. g. glacial acid and acetic anhydrid) can be partly neu-' tralized by treating the acid contaming liquid wit a neutralizin agent, such as sodium carbonate or an ydrous sodium acetate (which latter will react with the free sulfuric acid, with the liberation of acetic acid in place of the major portion of the sulfuric acid), always employing a quantity of the sodium compound or neutralizing agent insufficient for complete conversion of the free sulfuric acid into sodium bisulfate, that is to say employing for example 2 or 5 or 10 or,20% etc., less of the carbonate or acetate than would theoretically be necessary to convert all the free sulfuric acid contained in the acetylating mixture into bisulfate. In this way the reaction can be effected even at ordinary temperature, although it is sometimes necessary to slightly cool, and the more so the larger the amount of free sulfuric acid in the acetylating mixture, that is to say the more one diminishes the uantity employed, from the quantity t eoretically necessary of the sodium carbonate or acetate.

This process ofiers a great technical advantage, in that one can avoid the energetic coolin which is necessary in employing sulfuric acid alone. It is possible in some cases thus to proceed without artificial cooling or in any case to be able to regulate the reaction and the temperature by appropriate cooling, by means of water of ordinary temperature, and in some cases it ma be advantageous to heat in order to acce erate the reactlon, and even a strong heating if the quantity of free sulfuric acid remaining is very small. Instead of bisulfate of sodium, one can also employ other bisulfates such as bisulfate of potassium or of pyridin, etc.

The result of the present invention is the more surprising as in employing small quantities of sulfuric'acid alone, such as .5 ,or 1% or even 3% or more, and introducing the cellulose into the acetylatin mixture, although an acetylation takes p ace, there result more or less milky, gelatinous masses, more or less permeated with fibers, or briefly products which are absolutely useless. lf on the contrary one employs quantities of bisulfate of sodium representing togather with said small percentage of free S0 the quantity of sulfuric acid generally employed for a good acetylation, such for example as 15% sulfuric acid or more calculated upon the weight of the cellulose employed, solutions can be obtained which are very viscous and absolutely clearin giving products of the greatest value. y employmg bisulfate of sodium or other bisulfates as mentioned, it is possible to obtain without cooling cellulose acetates of the kind described in my application 103867, insoluble in chloroform and in mixtures of chloroform and alcohol by preci itating when a test portion shows this inso ubility, while by prolonging the reaction one can produce roduct's insoluble in chloroform but solube therein on addition of alcohol, of the nature described in my application 126502.

I have found that the em loyment of previously prepared sodium bisulfate or other bisulfates, that is to say the introduction of finished bisulfate into the acetylatin mixture of glacial acetic acid and acetic anhydrid presents difliculties, as the previous] prepared bisulfate can only be dissolved with great dilficulty and incompletely in the acetylating mixture. On the other hand if one prepares sodium bisulfate direct in the acetylating mixture for example by first introducing sulfuric acid in determined quantities, and afterward sodium acetate orcarbonate (anhydrous) a clear solution without any deposit whatever can be readily obtained.

The cellulose acetates obtained as hereinbefore described can be treated in accordance with the processes described in my application 126502 in order to change their solubilities whether the cellulose esters are precipitated from their solutions and submitted to a further treatment, or the reaction is allowed to proceed in the solution direct from the acetylation reaction, or any equivalent solution, which contains the said cellulose esters, insoluble in chloroform and in chloroform-alcohol or insoluble in chloroform, but soluble upon the addition of alcohol, after adding water or other agents capable of preventing further acetylization, but incapable of preventing the further reaction for the production of the changes in solubility. The amount of water used may be 5%, 10%, 20%, 30%,or 50%, or even more, depending-u on the particular solubilities desired, the quantity of water present having an efl'ect on the solubilities ,eveloped by the said treatment as explained in t e specification of my Patent 1217722.

E'wample.

An acetylating mixture prepared in the acetic acid, and 300 parts of acetic anhydrid are mixed with 15 to 18 parts of concentrated sulfuric acid, and to this mixture one adds 6.5 to 8 parts of anhydrous sodium carbonate (or an equivalent quantity of sodium acetate); into the solution thus ob tained 100 parts of cellulose (for exam le cotton, having a moisture content pre erably, but not necessarily, of about 3 to 6%) are introduced and the generation of heat by the reaction is regulated conveniently, by coolin with water. After the solution becomes 0 car, one can heat gently, for completing the reaction. The product, either 1n :1 precipitated form, or in solution, may be treated in thesame manner as described in in application 126502 or my Patent 1,217, 22.

W hat I claim and desire to secure by Letters Patent is 1. The herein described process of producing cellulose acetate, which comprises reacting upon cellulose with an acetylizing solution containing acetic anhydrid and a condensing a ent comprising a relatively large amount 0 a bisulfate and a relatively small amount of free sulfuric acid.

'2. The herein described process of producing cellulose acetate, which comprises reacting upon cellulose with an acetylizing solution containing acetic an'hydrid and a condensing agent comprising a relatively large amount of a bisulfate and a relatively small amount of free sulfuric acid, cooling in a less degree being employed the less the amount of free sulfuric acid present and even heating being employed in the case of very small quantities of free sulfuric ac1d.

3. A process of making cellulose acetate which comprises first (a) producing an acetylizing mixture by (a) mixing together acetic anhydrid, glacial acetic acid and sulfuric acid, (a adding thereto a material containing a neutralizing agent in a form capable of uniting with the sulfuric acid to form a bisulfate, said material being in amount suflicient to convert the major ortion only of the sulfuric acid into bisul ate and leaving a small amount of uncombined sulfuric acid (b) thereafter bringing cellulose and said acetylizing solution together, and (0) allowing the same to react,

4. A process of makin cellulose acetate which comprises first a) producing an acctylizing mixture by (a') mixin together acetic anhydrid, glacial acetic aci and sulfuric acid, (a) adding thereto a material containing a neutralizing agent in a form capable of uniting with the sulfuric acid to form a bisulfate, said material being in amount sufficient to convert the major ortion only of the sulfuric acid into bisul ate. and leavin a small amount of uncombined sulfuric acid, (b) thereafter bringing cellulose and said acetylizing solution together,

and (c) allowin the same to react, cooling in a less degree being employed the less the amount of free sulfuric acid present and even heating bein employed in the case of very small quantities of free sulfuric acid.

5. A process of making cellulose acetate which comprises first (as) producing an acetylizing mixture by (a) mixin together acetic anhydrid, glacial acetic acid and sulfuric acetate, (a adding thereto an amount of anhydrous sodium acetate capable of reacting with the sulfuric acid to convert the major part of the latter into sodium bisulfate, and leave a small amount of uncombined sulfuric acid, (b) thereafter bringing the cellulose and said acetylizing solution together, and (0) allowing the same to react, cooling in a less de ree being employed the less the amount 0% free sulfuric acid present, and even heating bein in the case of very sulfuric acid.

6. A process of makin cellulose acetate whichcomprises (a) pr ucing an acet-ylizing mixture by (a) mixing together 300 parts of acetic anhydrid. 400 parts of glacial acetic acid and 15 to 18 parts of concentrated sulfuric acid, ((1 adding thereto an amount of anhydrous sodium acetate, capable of reacting with the major portion only of the sulfuric acid and producing sodium bisulfa'te, (b) introducing into the acetylizing mixture thereby produced 100 parts of cellulose, (0) allowing the cellulose and acetylizin mixture to react cooling in a less degree ein employed the less the amount of free su furic acid present and even heating being employed in the case of very small quantities of free sulfuric acid.

7. In the process of making cellulose acetates, the herein described mode of preparing the acetylizing solution com risi producing a mixture of glacial acetic aci acetic anhydridand free sulfuric acid, and adding thereto a dry agent capable of reacting with sulfuric acid to form bisulfate, and which is added in amounts sufiicient tofprog employed small quantities of free *duce a bisulfate from the major part 0 t sulfuric acid present and to leave a relativalysmall amount of uncombined sulfuric acl 8. A solution comprising acetic anhydrid, glacial acetic acid, a. bisulfate and free sulfuric acid, in such proportions as to produce an acetylizing agent.

9. The herein described process of producing cellulose acetate, which comprises reacting upon cellulose with an acetylizing solution containing acetic anhydrid and a condensing agent comprising a relatively large amount of a bisulfate and a relatively small amount of free sulfuric acid and there after treating the so obtained cellulose acetate with an acid material in presence of water until the solubilities of the product in certain organic solvents have increased, the quantity of water present having an effect on the 'solu'bilities developed, and then stopping the treatment.

10. The herein described process of producing cellulose acetate, w ich comprises reacting upon cellulose with an acetylizing solution conta ning acetic anhydrid and a condensing agent comprising a relatively large amount of a bisulfate and a relatively small amount of free sulfuric acid, cooling in a less degree bein employed the less the amount of free sul uric acid present, and even heating being employed in the case of very small quantities of free sulfuric acid; and thereafter treating the so obtained cellulose acetate with an acid material in presence of water until the solubilities of the product in certain organic solvents have increased, the quantity of water present havin an efl'ect on the solubilities developed, an then sto 'ng the treatment.

11. The herein deseri ed process of producing cellulose acetate, which com rises reacting upon cellulose with an acety izing solution containing acetic anhydridand a condensing agent comprising a relatively large amount of a bisulf-ate and a relatively small amount of free sulfuric acid, and thereafter allowifig'the reaction mass ,to stand in presence of water, until the cellulose actetate acquires other desired solulbilities, and stopping the reaction while such desired solubi ities exist.

12. The herein described recess of producing cellulose acetate, w ich com rises reacting upon cellulose with an acety izing solution containing acetic anhydrid and a condensing agent comprising a relatively large amount of a bisulfate and a relatively small amount of free sulfuric acid, cooling in a less degree bein employed the less the amount of free sul uric acid present and even heating being emplotylgg in theease of very small quantities of sulfuric acid; and thereafter allowing the reaction mass to stand in presence of water until the cellulose acetate acquires other desired solubilities, the quantity of water present having an effect on the solu'bilities developed and sto ping the reaction while the desired soluhillties exist.

13. As a new product, a cellulose acetate insoluble in chloroform alone and insoluble in chloroform ugon'the addition of alcohol thereto, but solu 1e in acetone of the necessary concentration, the solubility in acetone of a given concentration being changed by the continued action of acid-containing materials. i

Testimony whereof I have hereunto subscribed my name.

Basel, 29th March, 19'15.

HENRY DR-EYFUS.

Corrections in Letters Patent No. 1,280,974.

It is hereby certified that in Letters Patent No. 1,280,974, granted October 8, 1918, upon the application of Henry Dreyfus, of Basel, Switzerland, for an improvement in "Cellulose Acetates and Processes of taking Same," errors appear in the printed specification requiring correction as follows: Page 2, line 72, for the word clearing rend clear; page 3, line 75, claim 5, for the word acetate" read acid; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 29th day of October, A. D., 1918.

[mun] R. F. WHITEHEAD,

Acting O'ommiuiomr of Palm. 

